Piezoactuators usually consist of several piezoelements arranged in a stack. Each of these elements in turn consists of a piezoceramic layer which is provided with metal electrodes on both sides. If a voltage is applied at these electrodes, the piezoceramic layer responds with a grid deformation which extends along a main axis to a useful longitudinal extent. Since this in turn amounts to less than 0.2% of the layer density along the main axis, a correspondingly higher layer thickness of active piezoceramic must be made available in order to achieve a desired absolute longitudinal extent. However, the voltage required for the actuation of the piezoelement rises with increasing layer thickness of the piezoceramic layer within a piezoelement. To keep this voltage within manageable limits, multilayer actuators are produced wherein the thickness of individual piezoelements is usually between 20 and 200 .mu.m.
Known piezoactuators of multilayer construction thus consist of up to a few hundred individual layers altogether. For their production, piezoceramic green foils are arranged in a stack in alternation with electrode material, and these are laminated and sintered together into a monolithic compound up to about 5 mm high. Larger actuators with larger absolute excursion can be obtained by gluing together several such stacks, for example. Only piezoactuators of fully monolithic multilayer construction have sufficiently high rigidities, particularly when large forces must be transmitted with the piezoactuator.
For the electrical contacting of such piezoactuators of multilayer construction, metallization strips are attached to the exterior of the piezoactuator, for example, or in a borehole in the middle of the surface of the individual actuator. To connect every second electrode layer with one of the metallization strips, for example, this must be insulated against the intervening electrode layers. This occurs easily in that every other electrode layer comprises a recess in the region of the one metallization strip, in which recess said electrode layer is not led to the metallization strip. The remaining electrode layers then comprise the recesses in the region of the second metallization strip, in order to enable a contacting with alternating polarity. Wires for the electrical connection are soldered to the metallization strips.
Piezoactuators whose alternating contacting occurs via recesses of the electrode layers are piezoelectrically inactive in the contacting zone, since an electrical field cannot build up there due to the one electrode that is missing, respectively. As a result, in the polarization as well as in the operation of the piezoactuator, mechanical tensions build in this piezoelectrically inactive contacting zone, which tensions can lead to tears in the inactive regions and thus at the metallization strips parallel to the electrode layers as well. This can lead to the complete splitting of the metallization strip and produces the result that, given punctate voltage supply to the metallization strips from outside, a part of the piezoactuator becomes dependent on the power supply and thus becomes inactive. The number of tears depends on the total height of the actuator and on the stability of the boundary surface between the inner electrode and the piezoceramic and can rise in continuous operation given alternating load conditions. Since, in the dynamic operation, a dynamic changing of the tears, or respectively, the tear openings also derives, the metallization strips are thereby further damaged during the operation of the actuator.